In a railway vehicle the various masses, such as body and bogies can exhibit undesirable oscillations, such as rolling, yawing and lateral movements. The wheel-sets, particularly, may oscillate undesirably in the lateral plane and excite oscillations of the other vehicle masses at certain speeds.
U.S. Pat. No. 4,067,261 discloses a railway truck in which the wheel treads are of relatively high effective conicity and each wheelset is resiliently suspended to the load-bearing means such that each wheelset is substantially self-steering, i.e. on curved track the wheelsets naturally align themselves along the radius of the curve and the correct rolling diameter between the inner and outer wheel is attained. This feature ensures that there is minimal wheel-tread and rail wear. Such wheelsets would normally tend to be highly unstable, i.e. oscillate seriously, on both straight or curved track because of the resilient suspension of the wheelsets and the forces generated by the tapered wheel-treads. However, the patent also teaches a coupling acting directly between the wheelsets which interconnects yawing movements of the wheelsets in opposite senses, i.e. 180.degree. out of phase with each other, so as to counteract this tendency to hunt by ensuring that, ultimately, hunting stabilizing creep forces are generated in the wheel-tread/rail contact areas. The coupling does not interfere with the self-steering characteristic of the wheelsets. The coupling extends substantially diagonally of the railway truck and may be in the form of diagonal linkages or articulated sub-frames. Such couplings ensure that wheelset stability is obtained even up to very high speeds.
In a bogie type vehicle some stability of each bogie frame is also obtained because of the inter-connection of the bogies to each other through the body and the connection of each bogie frame to the wheelsets and thence to the track. However, since with self steering bogies the connections between the frame and wheelsets are necessarily resilient with low stiffness in the longitudinal and lateral directions in order to achieve the natural self-steering of the wheelsets, the amount of stabilisation obtained through the interaction of the bogie frames via the vehicle body is insignificant and only the stabilising action between the wheelsets of each bogie is available and controls the maximum speed of the vehicle.
Another problem with the self-steering, stabilized railway trucks of the type mentioned above is that there can be longitudinal movements of the wheelsets relatively to each other and to the load-bearing means, such as during braking, because of the low longitudinal stiffness of the resilient elements connecting the wheelsets to the load-bearing means. The patent mentioned above discloses longitudinal anchors connecting the centre of yaw of each wheelset to the bogie frame to overcome this problem. These anchors have not proved to be acceptable in practice for two reasons. Firstly because of the problems and expenses of fitting a central bearing on each wheelset and the space considerations, and secondly because they have been found to have a destabilizing effect as they introduce a lateral connection between the wheelsets and the load-bearing means.
This invention seeks at least to minimise the above mentioned problems in a satisfactory manner without affecting the natural self-steering property of the wheelsets and the stabilizing action of the suspension.